Combustion apparatus



Nov. 22, 1966 o. A. oHLssoN 3,286,666

COMBUSTION APPARATUS Filed Nov. 3, 1964 2 Sheets-Sheet 1 UUIUIUI Hummm INVENTOR. OzOF' 67x54 O/fz. :so/V

Nov. 22, 1966 o. A. oHLssoN 3,286,666

COMBUSTION APPARATUS IN V EN TOR. Oro/r' #f-.4. Oz sse/v BMM United States Patent O 3,286,666 COMBUSTION APPARATUS Olof Axel Ohlsson, Stockholm, Sweden, assignor to AB Svenska Maskinverken, Kallhall, Sweden, a jointstock company of Sweden Filed Nov. 3, 1964, Ser. No. 408,536 11 Claims. (Cl. 110--28) This invention relates to combustion apparatus utilizing solid fuels and, more particularly, the invention is concerned with certain improved arrangements and means in that particular type of combustion apparatus in which there is provided an open-ended cyclone chamber of circular cross section in the draught system of a primary combustion chamber. In such an apparatus a heap or collection of solid fuels, such .as wooden chips or splinters, scrap wood, pieces of bark, peat, coal, garbage or the like, is kept burning within the primary combustion chamber in a manner to deliver an ample supply of hovering ignited fuel particles, mainly carbon particles, to the cyclone chamber in which the same will continue burning while catched in a cyclonically rotating stream of gases and air to produce hot and combustion gases discharging through the outlet end of the cyclone chamber in the form of a more or less extended flame.

ln the primary combustion chamber of such an apparatus the relatively coarse solid fuels are burned on a suitable grate through which sufficient quantities of primary air at a rather low pressure .are supplied to merely maintain a partial or incomplete combustion, the purpose of which is to effect drying and partial decomposition of the original fuel so that minut-e particles which will readily hover and hence follow the draught into the cyclone chamber will be formed. Since it is important that these particles do not become extinguished during their passage from the primary combustion chamber into the cyclone chamber, the latter must be located close to the primary combustion chamber and may advantageously form a direct open extension thereof although it may also be separated therefrom by more or less constricted but rather short passages.

In the cyclone chamber there is maintained a cyclonically rotating stream of gases and air by introducing additional air or a gas mixture, at a high velocity through nozzles or tuyres opening in a lsubstantially tangential direction through the circular cyclone chamber wall. The burning fuel particles received from the primary combustion chamber will be catched in this stream and continue to burn therein and, while doing so, the fuel particles will, -of course, besubjected to rather strong centrifugal forces due to the high rotational speed of the gases so that all the unconsumed fuel particles will tend to move radially outwards towards the cyclone chamber wall `and concentrate in la rotating layer of limited radial thickness where a certain separation will take place and in which an extreme heat is developed so that complete combustion can be promoted, provided that the unconsumed fuel particles are -retained in this layer or zone for a sufficiently long period of time.

During the continued burning of the hovering fuel particles Within the cyclone chamber there will be produced rather large quantities of hot exhaust gases containing a certain, and frequently considerable, amount of combustible gaseous components driven off from the fuel Iand when these exhaust gases are discharged through the outlet end of the cyclone chamber they will form a flame in which final combustion of the gases is effected, possibly under additional supply Vof fresh air 4'if required. This flame is commonly used to heat a boiler or like equipment located immediately outside the outlet end of the cyclone chamber and suitably designed to utilize the lCC 1 radiated heat from the flame as well las the convected heat from the hot gases.

Considerable losses may occur if unburned fuel or carbon particles leave the cyclone chamber and also from other points of view it is highly desirable that the gases discharged from the outlet end of the cylone chamber are substantially free from heavier impurities which, of course, may clog the flues, cause uncontrolled fires therein and foul the outside air. In order to obtain a maximum efficiency of the entire plant it is thus necessary to provide a combustion -apparatus of the kind described in which the airborn fuel particles are retained in the cyclone chamber for a sufficiently long time to be completely consumed.

It is a main object of this invention to provide means in a cyclone chamber of the type referred to for improving the possibilities to prevent escapement of fuel or carbon particles through the outlet end of the cyclone chamber. Another object of the invention is to make it possible to reduce or even entirely omit the expensive .structural constriction of the outlet end of the cyclone chamber which has hitherto been considered necessary for the very same purpose.

Still .another object of the invention is to provide improved means for introducing air into the cyclone chamber in order to maintain the cyclone of gases therein and for making it possible to continuously check the burning conditions within the cyclone chamber without interrupting the operation of the combustion apparatus.

With these and other objects in view the invention mainly consists in that at lea-st some of the air inlet nozzles or tuyres of the cyclone chamber are located adjacent the outlet end of the cyclone chamber and are directed to expel the ai-r supplied therethrough in a helical direction relatively to the circular interior wall of the cyclone chamber and Iaway from said outlet end thereof. To obtain best results with .such a tuyre arrangement it has been found necessary to operate with a certain minimum air pressure depending on the internal diameter of the cyclone chamber and amounting to `approximately 1 millimeter water column pro each millimeter of said internal diameter. It has also been found most appropriate to use certain types of nozzles or tuyres in order to obtain concentrated jets of air into the cyclone chamber as will be described hereinafter.

For further elucidation of the invention reference will now be had to the accompanying drawings, wherein:

FIG. 1 is a sectional elevation of a first form of aeombustion apparatus embodying the invention,

FIG. 2 is a cross section of thesame apparatus taken along the line 2 2 in FIG. 1,

FIG. 3 is a sectional elevation of a modified form of cyclone chamber wlhich may replace the cylindrical cyclone chamber in the apparatus of FIG. l,

FIG. 4 is a sectional elevation of another modified form of cyclone chamber,

F'IG. 5 is a sectional elevation of still another modified form of cyclone chamber,

FIG. 6 is a longitudinal sectional elevation of a second form of a combustion apparatus embodying the invention, FIG. 7 is a fragmentary out-side view of a cyclone chamber wall with an air lsupply jacket for the tuyres, and

FIG. 8 is a cross section of a cyclone chamber wall l in the centre of the 4grate 11 so that they will spread substantially evenly over the grate. The air blown into the bottom compartment 12 will pass through the annular openings of the Igrate and hence through the heap or layer of fuel and when the latter has been set on re it will readily continue -burning although the supply of primary air through the conduit 13 is restricted to only maintain a partial or incomplete combustion thereof. As a result of this primary combustion the fuel on the grate will dry and decompose by lcarbonization so that a considerable amount of small burning fuel particles will form. Since these particles are small, dry and light they will easily hover and follow the draught rfrorn the primary combustion chamber into the next section of the combustion apparatus which is a so called cyclone chamber 15.

f The cyclone chamber of the combustion apparatus shown in FIGS. 1 and 2, which is cylindrical and openende-d, has a wall 16 of refractory material and forms a vertical upper extension of the primary combustion chamber 10. The height of the cyclone chamber should preferably be -at least the same las the inside diameter thereof which in turn may be chosen rather arbitrarily although it should for structural reasons preferably not exceed the inside diameter of the primary combustion chamber.

Adjacent the upper end off the cyclone chamber 15 there is provided an annular air jacket or duct 17 around the outside of the wall 16 and air under pressure is supplied to the interior of this jacket through a conduit 18. A plurality of tapering nozzles or tuyres 19 of a type which will be described hereinafter extend through the wall 16 of the cyclone chamber :from the interior of the jacket 17 to carry the air under pressure therefrom into the cyclone chamber and eject it there in the form of concentrated jets. As will be seen from FIGS. l and 2 the nozzles or tuyres 19 lare equally spaced around the wall 16 and all arranged in the same manner to expel the air in a counterclockwise direction and substantially tangentially to the interior wall of the cyclone chamber. As will be seen from FIG. 1, however, the nozzles or tuyres do not extend horizontally but are each slightly inclined so that the air jets theretfrom will tend to follow a helical path downwardly over the wall 16.

The inclination of each nozzle or tuyre should be so chosen that all the ai-r expelled therethrough is caused to spread out over the cyclone chamber wall below an imaginary horizontal line drawn through the tuyre openings 20 in the inside of the wall 16. Consequently the minimum inclination depends on the capability of the tuyre to concentrate and direct the air jet. yIt is in other words important that the air supplied through the nozzles or tuyres does not in any way impart a motion towards the upper outlet end of the cyclone chamber to the gases therein.

If these conditions are fulfilled there will be maintained a cyclonically rotating stream of gases in the cyclone chamber 15 in which the hovering and still burning fuel particles fr-omthe primary combustion chamber 10 will be catched and retained until they yare completely consumed and the gases leaving the upper end 15 of the cyclone chamber 15 will be practically free from all unburned fuel particles in spite of the tfact that there is no -structural constriction in the said upper end. This rather surprising result may be explained by the fact that the downwardly inclined air jets have a certain ejector effect on the gases trying to nd their way out through the upper or outlet end of the cyclone chamber and particularly on the radially outer sheets of such gases in which suspended solid particles are most likely to concentrate. These outer sheets of gases will consequently become sucked back from the outlet opening and again travel downwards through the cyclone chamber.

On the other hand the pure and very hot gases produced in the cyclone chamber burning process will collect in the centre of the cyclone chamber and will hence be very little affected by the lair jets through the nozzles or tuyres 19. These gases will consequently discharge through the central portion of the upper ou-tlet opening 15' of the cyclone chamber where they will form a more or less extended flame of intense heat in which all the combustible gaseous components are readily consumed. In order to utilize the radiated heat from Isaid iiame to a maximum degree the heat absorbing walls 21 of the boiler or similar equipmment connected to the combustion apparatus may advantageously be extended to surround a flame room 22 above the upper end orf the cyclone chamber 15 as shown in dash-and-dot lines in FIG. 1 but, alternatively, such a llame room may -be surrounded by any suitable walls or even by an extension of the wall 16.

As will be seen from FIGS. 1 and 2 the air jacket or `d'uct 17 is yform-ed between upper and lower anges 23 and 24 respectively extending radially outwards from the outside of the cyclone chamlber wall 16.- `In this particular case the radially outer wall of the vjacket 17 is formed by a portion olf a boiler supporting wall structure 25 surrounding the entire combustion apparatus. As will be explained more in detail in connection with FIGS. 7 and 8 sleeves 26 are mounted in Isaid outer wall of the jacket 1'7-one for each nozzle or tuyre 19 and in line therewith-and these sleeves are tted in corresponding holes in the wall 25. Each sleeve 26 has at its outer end a rem-ovalble ca'p 27 provided with a central opening covered by a pane orf' glass through which -it is possibile to look through the related nozzle or tuyre all into the cyclo-ne chamber 15 and thus check the hurning conditions therein withfout interrupting the operation of the combustion apparatus.

It will Ibe obyious that the inclined nozzles or tuyres may advantageously be used also in cyclone chambers which have a more or lless constricted outlet end. In such cases they will effectively assist in the production of stilll purer output gases and they will also', as in the case shown `in FIG. 1, lfacilitate a uniform distribution of the air in the cyclone chamber and hence promote a rapid and effective consumption of the .gas suspended fuel particles. Consequently the cylindrical cyclone chamber 15 in FIG. l may, iff desired, be replaced by any other suitable form olf cyclone chamber section. For the purpose of illustration three anbitrarily chosen forms of such differently shaped cyclone chamber sections are shown in FIGS. 3, 4 and 5.

In FIG. 3 a .fausto-conical constriction 28 has been provided at the upper end of the circular wall 16a surrounding the cyclone chamber. It sh-ould be understood, however, that the frusto-conical constriction could as well be replaced -by a flat, annular, -i.-e. truly radial, constriction ange, if so desired.- In FIG. 4 the wall 16b of the cyclone chamber tapers gradually upwards so that the upper outlet end opening of the cyclone chamber is` considerably smaller in diameter than the lower end opening. In FIG. 5 the wall 16a` is vertically curved so that the cyclone chamber will be substantially sphericalin shape. The nozzle or tuyre arnangement as well as the air jacket in 1each of the FIGS. 3, 4 and 5 is substantiafl-ly the same as in FIG. 1 and therefore a repeated description of these details is believed unnecessary. Similar parts have 4simply 'been given the same reference numeral as in FIG. 1 with the addition of the letter a in FIG. 3, the Eletter b in FIG. 4 and the letter c in FIG. 5. All the differently shaped cyclone chambers preferably have walls with good heat insulating and refractory properties to reduce heat losses 4from the rapidly rotating layer of tfuel particles and promote a rapid consumption thereof.

In FIG. 6 there is shown another form of a combustion' apparatus embodying the invention. This modified apparatus presents a primary combustion chamber 30 into which the vsolid fuel is introduced from a'bove through a closable charging hopper 31. The fuel is burned on a grate 32 extending over a bottom compartment 33 into which primary air is blown at a Irather 'low pressure and in limited quantities. The burning conditions maintained in the primary combustion chamber 30 are thus essentially the same as already described in connection with FIGS. 1 and 2.

'Ilhe hovering and still burning fuel particles produced in the primary combusti-on chamber 30 will follow the draught through a constricted opening 34 in the rear wail of the primary combustion cham-ber and thus enter the cyclone chamber 35 slightly offset to the centre thereof. The cyclone chamber 35 differs from the cyclone charn- 'bers already described hereinbefore mainly by the fact that its axis is horizontal but also in that it is slightly conical having its largest diameter at the outlet end. It should be understood that a cy-clone chamber of the kind referred to in this description cou-fl-d in fact occupy any desired position, .i.e. Ibe vertical, horizontal or inclined, and the outlet end thereof could even point downwards if so required in certain installations, without the operation thereof being in any way affected.

The 'burning fuel particles entering the cyclone chamber 35 of FIG. 6 will be lcatehed in a cyclonically rotating stream of gases produced by injecting air under relatively high pressure th-rou'gh a series of inclined nozzles or tuyres 36 similar to those already described in connection with FIGS. l and 2. The air is supplied to the tuyres through a conduit 37 and an annular jacket 38 surrounding the wall 39 of the cyclone chamber adjacent the outlet end of the latter. As already mentioned, the outlet opening 35' ofthe cyclone chamber 35 is` slightly larger in diameter than the left hand, inner end thereof and the flame forming gases discharged therethrough are utilized to heat a boiler 40 or the like.

`It should be emphasized that the proper operation of the tuyre arrangement and hence of the cyclone chamber is highlly dependent on that a sufficiently high pressure is used on 'the air injected through the tuyres and that air at such pressure is availa'b-le in sufficient quantities. It has 'been found by experience that the air pressure must not come substantially below 1 millimeter water column height .for each millimeter of the inside diameter of the cyclone chamber. In practice a cyclone chamber frequently has a diameter of up to or even beyond 4 meters and in such cases particular types of heavy duty blowers or rotary compressors will be needed.

It should also be understood that, instead of fresh air, any mixture of -gases for example containing flue gases, steam or the like may be injected through the tuyres. The air or gas mixture may advantageously be preheated -in any suitable manner.

In FIGS. 7 and 8 there is illustrated a preferred form of a tuyre and air jacket arrangement used in connection with the cyclone chamber of FIG. 6. As will appear particularly from FIG. 8 there is provided a projection 41 on the outside of the cyclone chamber wall 39 for each tuyre and 'a hole 42 is provided in said projection for receiving a lining tube 43 extending in the proper direction relative to the inside of the wall 39. In the lining tube 43 a gradually tapering sheet metal nozzle 44 having an external flange 45 at its Wider end is inserted from the outside. It is highly important that the nozzle 44 is of considerable length in relation to its diameter and that the inside diameter of the nozzle is slowly and uniformly decreasing towards the inner end. The nozzle 44 may be retained in the lining tube 43 by any suitable means if the pressure of the air within the jacket 37 should not be capable of keeping it in place which it usually is. In any case the nozzle should be -removable so that it may be replaced Whenever necessary.

In order to permit replacement of the nozzle 44 there is provi-ded a tubular extension 46 in the radially outer rwall of the housing or jacket 37 and this extension is carefully aligned with hole 42 and the nozzle 44 as shown. To prevent the escapement of air the outer end of the tubular extension 46 hlas a removable end cap or lid 47 in which there is mounted a glass pane 48. By looking through this glass pane 48 and through the nozzle 44 it will be possible to frequently che-ck the burning conditions in the cyclone chamber without in any way changing the operating conditions thereof and it is also possible to ind out whether the nozzle 44 is still in good condition or not.

In all essential respects the air jacket and tuyre arrangement used in FIGS. 1-5 is of the same preferred type as now described with reference to FIG. 7 and 8, it being only adapted to fit the slightly different environment. All the tuyres are preferably evenly spaced along the circumference of the cyclone chamber at substantially one and the same radial plane thereof which in the simplest way 'will assure a most uniform distribution of the air expelled through the tuyres. The number of tuyres may, of course, vary particularly with the diameter of the cyclone chamber and with their jet concentrating capability.

Although a few specific embodiments of the invention have been particularly shown and described hereinbefore for the purpose of illustration it should be understood that the invention must not in any way be considered limited thereby. Several changes and modifications may thus be made without departing from the scope of the appended claims.

I claim:

1. In -a combustion apparatus, in combination: a primary combustion chamber having means for introducing and burning relatively coarse solid -fuels therein in a manner to produce an ample supply of hovering solid fuel particles most of which are in an ignited condition, an open-ended cyclone chamber of circular cross section lcommunicating with said primary combustion chamber in a manner to receive said hovering fuel particles therefrom while most of them are still burning, said cyclone chamber having an outlet end opening into a heat consuming appara-tus, a plurality of gas inlet tuyres opening into said cyclone chamber in a substantially tangential direction and means for introducing glas through said tuyres into said cyclone chamber in a manner to produce therein :a cycloni-cally rotating stream of gases capable of catching said hovering fuel particles emanating from said coarser solid fuels burned in the primary combustion chamber, a plurality of said gas inlet tuyres being located in the vicinity of the outlet end of said cyclone chamber and being each disposed at 1an Iangle to a radial plane which is perpendicular to the axis of said cyclone chamber to expel the gas supplied therethrough in a helical direction relatively to the circular interior wall of said cyclone chamber and away from the outlet end thereof.

2. In a combustion apparatus rthe combination as claimed in claim 1, wherein said gas inl-et tuyres located in the vicinity of the outlet end of said cyclone chamber are substantially evenly distributed around the circumference -of the cyclone chamber and have their openings into the cyclone chamber located in substantially the same radial plane thereof.

3. In a combustion apparatus the combination as claimed in claim 1, wherein each of said gas inlet tuyres located in the vicinity of the outlet end of said cyclone chamber comprises an elongated, tapering gas inlet nozzle having its narrower end pointing inwardly relative to said cyclone chamber and having an inside diamete-r at its narrower end which is only a small fraction of the length of the nozzle.

4. In a combustion apparatus the combination as claimed in claim 1, wherein each of said gas inlet tuyres located in the vicinity of the outlet end of said cyclone chamber comprises a tapering gas inlet nozzle exchangeably mounted on an opening in the wall of the cyclone chamber and having its outer end communicating with a conduit supplying gas under pressure.

5. In -a combustion apparatus the combination as claimed in claim 1, wherein said means for introducing gas ithrough said tuyres located in the vicinity of the outlet end of said cyclone chamber comprises a source of gas capable of delivering glas to said tuyres at a pressure which, when expressed in water column height, is at least substantially equal to the inside diameter of said cyclone chamber at the location of said tuyres.

6. In a combustion apparatus utilizing solid fuels, in combination: a primary combustion chamber having a grate at its bottom, an exit for combustion lproducts above said grate, means for supplying coarse solid fuels to said grate and means for delivering air through said grate in a manner to effect partial combustion of said coarse solid fuels thereon and to produce an ample supply of small, incompletely consumed, ignited solid fuel particles rising from said coarser fuel on the grate with the gaseous cornbustion products therefrom; an open-ended cyclone chamber of circular cross section forming an extension of said exit of said primary combustion chamber and receiving said combustion products including said airborne fuel Iparticles while most of the latter are still burning, said cylone chamber having an outlet end opening into a heat comsuming apparatus, a plurality of -air inlet tuyres opening approximately tangentially into said cyclone chambei in the vicinity of the outlet end thereof and each being inclined with respect to a radial plane perpendicular to the axis of said cyclone chamber to expel the air supplied through said tuyres in a helical direction away from said outlet end of the cyclone chamber and close to the circular interior wall thereof, all said tuyres pointing in substantially the same approximately tangential direction relative to the axis of the cyclone chamber and being substantially evenly distributed along the circumference thereof, and means for supplying air to said tuyres under -a sufficiently high pressure to produce in said cyclone chamber a cyclonically rotating stream of gases capable of catching and effectively separating said airborne burning fuel particles emanating from said coarser solid fuels burned on the grate in the primary combustion Vchamber from the gaseous combustion products carrying them into the cyclone chamber and also capable of retaining said fuel particles in a rapidly rotating layer near the interior wall of and inside the outlet end of the cyclone chamber until they are completely consumed.

7. In a combustion apparatus the combination as claimed in claim 6, wherein said cyclone chamber has a heat insulating wall of refractory material.

8. In a combustion apparatus the combination as claimed in claim 6, wherein said cyclone chamber has an outlet end opening the -inside diameter of which is at least the same as the maximum inside diameter of the remaining part of the cyclone chamber.

9. In a combustion apparatus the combination 'as claimed in claim 6, wherein said cyclone chamber is frusto-conical and has its relatively wider end connected to said exit of .the primary combustion chamber to receive said airborne fuel particles therefrom.

10. In a combustion apparatus utilizing solid fuels, in combination: a primary combustion chamber having a grate near its bottom, an eXit for combustion products above said grate, means for supp-lying relatively coarse solid fuels to said grate and means for delivering air through said grat-e at a low pressure to effect partial comlbustion of said relatively coarse solid fuels thereon in a manner so that there is obtained therefrom a plurality of small incomplete-ly consumed, ignited `solid fuel particles capable of hovering in the gaseous combustion products Vseeking their way out through said exit; an open-ended cyclone chamber of circular cross section having its inlet end connected to said exit of the prima-ry combustion chambei to `receive said combustion products including said airborne fuel particles therefrom while most of said particles are still burning, said cyclone chamber having an outlet end opening into a heat consuming boiler, an annular series of gas inlet tuyres arranged in the vicinity of the outlet end of said cyclone chamber and all pointing in the same circumferential direction relative to said cyclone chamber, each of said tuyres comprising an elongated, Itapering nozzle penetrating the wall of said cyclone chamber in a direction which is closely tangential to the interior wall of said cyclone chamber at the point where the narrower inner end of -said nozzle opens into the cyclone chamber, each of said nozzles being also tilted in relation to an imaginary radial plane perpendicular to the axis of said cyclone chamber to direct the gas passing therethrough away Ifrom said outlet end of the cyclone chamber in -a helical fashion, and means for delivering gas to the outer ends of said nozzles at a pressure which, when expressed by the height of a column of water, is at least substantially equal to the inside diameter of said cyclone chamber at the location of said series of tuyres.

11. In a combustion apparatus the combination as claimed in claim 10, wherein said cyclone chamber has an interior cross sectiona-l area at its inlet end which is smaller than the area of said grate in the pri-mary combustion chamber.

References Cited by the Examiner UNITED STATES PATENTS 1,530,321 3/1925 Pollock 1l0-28 l1,722,496 7/ 1929 Chapman 122-5 1,767,952 6/1930 Wollaston 110-31 2,216,117 10/1940 Krug 110-28 2,923,260 2/1960 Rummel 110-28 FOREIGN PATENTS 797,029 6/ 1958 Great Britain. 852,667 10/ 1960 Great Britain.

CHARLES I. MYHRE, Primary Examiner. 

1. IN A COMBUSTION APPARATUS, IN COMBINATION: A PRIMARY COMBUSTION CHAMBER HAVING MEANS FOR INTRODUCING AND BURNING RELATIVELY COARSE SOLID FUELS THEREIN IN A MANNER TO PRODUCE AN AMPLE SUPPLY OF HOVERING SOLID FUEL PARTICLES MOST OF WHICH ARE IN AN IGNITED CONDITION, AN OPEN-ENDED CYCLONE CHAMBER OF CIRCULAR CROSS SECTION COMMUNICATING WITH SAID PRIMARY COMBUSTION CHAMBER IN A MANNER TO RECEIVE SAID HOVERING FUEL PARTICLES THEREFROM WHILE MOST OF THEM ARE STILL BURNING, SAID CYCLONE CHAMBER HAVING AN OUTLET END OPENING INTO A HEAT CONSUMING APPARATUS, A PLURALITY OF GAS INLET TUYERES OPENING INTO SAID CYCLONE CHAMBER IN A SUBSTANTIALLY TANGENTIAL DIRECTION AND MEANS FOR INTRODUCING GAS THROUGH SAID TUYERES INTO SAID CYCLONE CHAMBER IN A MANNER TO PRODUCE THEREIN A CYCLONICALLY ROTATING STREAM OF GASES CAPABLE OF CATCHING SAID HOVERING FUEL PARTICLES EMANATING FROM SAID COARSER SOLID FUELS BURNED IN THE PRIMARY COMBUSTION CHAMBER, A PLURALITY OF SAID GAS INLET TUYERES BEING LOCATED IN THE VICINITY OF THE OUTLET END OF SAID CYCLONE CHAMBER AND BEING EACH DISPOSED AT AN ANGLE TO A RADIAL PLANE WHICH IS PERPENDICULAR TO THE AXIS OF SAID CYCLONE CHAMBER TO EXPEL THE GAS SUPPLIED THERETHROUGH IN A HELICAL DIRECTION RELATIVELY TO THE CIRCULAR INTERIOR WALL OF SAID CYCLONE CHAMBER AND AWAY FROM THE OUTLET END THEREOF. 